depend on/upon

We're not sure if we'll have the picnic. It depends on the weather. [=if the weather is good we will have the picnic]

“Will you go back to college?” “I don't know. It depends on whether or not I can afford it.”

The stamp's value depends on how rare it is.

Depending upon your child's weight and height, she or he may have to sit in the back seat of the car.

It's not clear how many people were at the rally. Reports vary between 10,000 and 20,000, depending on who's counting. [=some people report that there were 10,000 people at the rally, others report that there were 20,000]